Soil model in FreeCAD FEM

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ebrahim raeyat
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Soil model in FreeCAD FEM

Post by ebrahim raeyat »

Hi All. I wanted to model soil with FreeCAD. with which element/is I can simulate soil? can I model soil with springs? can I model uplift in soil? If yes, with which element/s?
Thanks.
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NewJoker
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Re: Soil model in FreeCAD FEM

Post by NewJoker »

Unlike Abaqus, CalculiX doesn’t have any built-in functionalities made specifically for analyses of geotechnical problems. For example, there are no material models such as Drucker-Prager, Mohr-Coulomb or clay plasticity. However, it’s possible to bypass many of these limitations. For instance, you could define your own material model (one of those mentioned above or other) via UMAT subroutine. In fact, Drucker-Prager model is used as an example for UMAT definition in the documentation.

In this case, apart from material model, you probably won’t need other special-purpose functionalities and standard analysis steps, interactions and element types should be sufficient.
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ebrahim raeyat
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Re: Soil model in FreeCAD FEM

Post by ebrahim raeyat »

NewJoker wrote: Wed Oct 20, 2021 11:24 am Unlike Abaqus, CalculiX doesn’t have any built-in functionalities made specifically for analyses of geotechnical problems. For example, there are no material models such as Drucker-Prager, Mohr-Coulomb or clay plasticity. However, it’s possible to bypass many of these limitations. For instance, you could define your own material model (one of those mentioned above or other) via UMAT subroutine. In fact, Drucker-Prager model is used as an example for UMAT definition in the documentation.

In this case, apart from material model, you probably won’t need other special-purpose functionalities and standard analysis steps, interactions and element types should be sufficient.
Thanks for your reply. Is there any example?
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bernd
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Re: Soil model in FreeCAD FEM

Post by bernd »

harryvL has done some soil analysis and has explained a lot in this regard. There should be some forum posts in this regard. But I am on a mobil so it is rather difficault to search the forum.
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NewJoker
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Re: Soil model in FreeCAD FEM

Post by NewJoker »

In this thread you can find some examples involving soil mechanics:
https://forum.freecadweb.org/viewtopic. ... l&start=90
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ebrahim raeyat
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Re: Soil model in FreeCAD FEM

Post by ebrahim raeyat »

bernd wrote: Thu Oct 21, 2021 8:40 am harryvL has done some soil analysis and has explained a lot in this regard. There should be some forum posts in this regard. But I am on a mobil so it is rather difficault to search the forum.
I had been searched a lot, but did not find this topic, although I had been see in past. thanks to you bernd and @NewJoker
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eccioloste
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Re: Soil model in FreeCAD FEM

Post by eccioloste »

Hello! I have been reading HarryL's work in the subforum page "fcFEM - FEA from start to finish". He was taking on a challenging task unfortunately he stopped working on it.

I have been working with calculix latelyto try and model soil. I found out that Calculix has a Mohr-Coulomb material model imported from ABAQUS

Preparing the inp .requires some editing outside freecad, but if I can get it to work then anybody can.

Code: Select all

* user material provided with calculix launcher

**     par1=Young's modulus, E
**     par2=Poisson's ratio, nu
**     par3=cohesion, c
**     par4=friction angle, phi [degrees] Cannot be set to zero
**     par5=dilation angle, psi [degrees] Cannot be set to zero


*MATERIAL,NAME=ABAQUSMCWD
*USER MATERIAL, CONSTANTS=5
<par1>,<par2>,<par3>,<par4>,<par5> 

*DENSITY
----       
While working on this simple model, I encountered a serious issue with freecad mesh output. My model was supposed to be 2d on the xz plane, but as i read the calculix .inp file, node y coordinates were not zero but were given a very small number instead (something like e-11)... this would affect my model.
I corrected manually the y values to 0 and the output was definetly different.
project_freecad.JPG
project_freecad.JPG (52.51 KiB) Viewed 5096 times
this is the calculix output without editing the mesh
calculix_output_1.JPG
calculix_output_1.JPG (177.5 KiB) Viewed 5096 times
this is the output after editing the mesh
calculix_output_with_y_fixed.JPG
calculix_output_with_y_fixed.JPG (106.18 KiB) Viewed 5096 times
I am working on evaluating different elements in the analysis.

Any suggestion is more than welcome!
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ebrahim raeyat
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Re: Soil model in FreeCAD FEM

Post by ebrahim raeyat »

bernd wrote: Thu Oct 21, 2021 8:40 am harryvL has done some soil analysis and has explained a lot in this regard. There should be some forum posts in this regard. But I am on a mobil so it is rather difficault to search the forum.

Hi bernd. As I completed my creation of automatic foundation geometry model ( geometry and forces comes from CSI ETABS Software), I wanted to model the soil under foundation with simple springs, not real soil. my problem is 2D. I model the foundation with shell thick element and soil with spring (like winkler model). can I do it with Calculix in FreeCAD? or I must do it with something else like OpenSees?

I wanted this to be usable for end users, not only for mine.

I can produce OpenSees Input .tcl file probably, but I want to know, can I show the stress of soil under foundation?
I mean can be done all of proccess in Python?
because I don't know c++ and don't know how can I compile FreeCAD in Windows!

related topics:
https://forum.freecadweb.org/viewtopic. ... 19#p551619
https://forum.freecadweb.org/viewtopic. ... 72#p552072

thanks.
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ebrahim raeyat
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Re: Soil model in FreeCAD FEM

Post by ebrahim raeyat »

bernd wrote: pinged by pinger macro
NewJoker wrote: pinged by pinger macro
I wanted a spring like constraint that share two nodes in the same location. I found two constraint for creating foundation on soil, I mean the spring under foundation, constraint contact and constraint tie. As I found it needed the two surface with small gap between them to generate mesh nodes correctly. is it correct?

https://forum.freecadweb.org/viewtopic. ... 30#p589130
thschrader
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Re: Soil model in FreeCAD FEM

Post by thschrader »

ebrahim raeyat wrote: Sun Apr 17, 2022 6:40 am ...
As I found it needed the two surface with small gap between them to generate mesh nodes correctly. is it correct?
Yes, you are right.
There must be a tiny gap between the contact surfaces, otherwise you get coinzidental meshnodes.
In this case the gap is 0,01 mm.
See file (ccx-runtime approx 3 min):
3pointcontact.FCStd
(36.7 KiB) Downloaded 37 times
gap.JPG
gap.JPG (57.62 KiB) Viewed 2406 times
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